There are countless uses for laminated films which exhibit good fluid absorbency as well as fast wicking properties. Such laminated films are useful in the manufacture of diapers, paper towelling, bandages, surgical pads, tissues and the like. Usually a laminated film of this type provides one of the above desired properties but not both. Normal preparation of absorbent laminated films involves making an absorbent water dispersion of the absorbent composition, laying down a thin wet film, drying the same and then applying it to an appropriate tissue layer or layers.
Hydrolyzed starch polyacrylonitrile graft copolymers which exhibit the capacity to absorb from about 300 to 1000 times their weight of deionized water are known at this time. The development of these compositions was carried out by the Northern Regional Research Laboratory at Peoria, Ill. Starch polyacrylonitrile graft copolymer is produced by the free radical method of polymerization. In this method, starch, either gelatinized or ungelatinized, is exposed to a catalyst such as ceric ammonium nitrate which acts as a catalyst to generate free radicals in the starch chain. These free radicals can also be produced by radiation. Polyacrylonitrile chains become attached to these free radicals by copolymerization. A wide range of substitution in these copolymers is known in the art. For example, U.S. Pat. No. 3,035,099 shows a preparation of copolymers in which the starch to polyacrylonitriles molar ratios range from 1:1.5 to 1:9. The variations in molar ratio of the components of the copolymer is not critical to the practice of this invention. The resulting material is then saponified to hydrolyze the polyacrylonitrile chains to carboxy amide and alkali metal carboxylate groups mixed with metal salts. Drying the hydrolyzed material can be accomplished by tumble air drying or vacuum drying. After drying, the material can absorb about 300 to 400 times its weight of deionized water. Washing the absorbent polymer before drying with alcohol increases its absorbency to 800 to 1,000 times its weight of deionized water.
To use this absorbent copolymer as part of a laminated film in such products as towelling, diapers, bandages, surgical pads, tissues, etc. the hydrolyzed starch polyacrylonitrile graft copolymer which is normally in powder form is formed into a thin film. To do this, it is first dispersed in water, then sheared to a small size, layed down as a wet film and finally dried. The resulting product is a thin film of absorbent material which is then applied directly to backing tissues to form a laminated film comprising the backing tissues and the absorbent material. Although this resulting product is generally highly absorbent, the wicking properties are somewhat reduced because of the reduced surface area between adjacent particles of the absorbent polymer and because of blocking caused by the highly absorbent polymer material. Further, the cost of preparing laminated absorbent film in the above manner is quite expensive. Accordingly, there is a need for an absorbent composition usable in the preparation of absorbent laminated film of the type which retains its fast wicking properties as well as its high absorbent characteristics.